Known techniques in the related art for drying water-containing solid fuel, such as biomass, include those disclosed in the Patent Literature described below.
The related art disclosed in Patent Literature 1 is a method of drying biomass utilizing sensible heat of combustion exhaust gas, wherein moisture is separated from the combustion exhaust gas with a condenser after drying and the gas is mixed with combustion air and supplied to a boiler.
The related art disclosed in Patent Literature 2is a steam heat-pump drying apparatus provided with a switching valve in a steam compressor system that is configured so as to perform a drying operation through a steam heat-pump cycle and a through-flow drying operation, as well as an operating method thereof. In this case, the valve is opened/closed in accordance with the water content of a material to be dried; when drying a material with high water content, drying is performed with vapor; and, when drying a material with low water content, through-flow drying is performed.
The related art disclosed in Patent Literature 3is an evaporator in which escape control for adjusting pressure is carried out at a compressor outlet and a drain trap is provided at a condenser outlet. This evaporator has enhanced thermal efficiency by providing, in addition to employing a steam compressor, a heat exchanger for performing heat exchange between compressor-inlet gas and compressor-outlet gas and, furthermore, utilizes sensible heat of a noncondensable gas to preheat the raw material by circulating the noncondensable gas in the system, thereby promoting heat conduction and lowering the drying temperature.